removeInvalidFieldConfigSchemesForIssueType

Given an issueType, this method will correctly remove the fieldConfigSchemes if necessary. In other words
if a FieldConfigScheme is linked to only a single issueType, and we're deleting that issuetype then that
FieldConfigScheme will be deleted. If a FieldConfigScheme is associated with multiple issueTypes, then only
the association for the issueType we're deleting will be removed, but the FieldConfigScheme will remain.

removeInvalidFieldConfigSchemesForCustomField

Given a CustomField, this method will correctly remove the fieldConfigSchemes if necessary. In other words
if a FieldConfigScheme is linked to only a single CustomField, and we're deleting that field then that
FieldConfigScheme will be deleted. If a FieldConfigScheme is associated with multiple fields, then only
the association for the field we're deleting will be removed, but the FieldConfigScheme will remain.

getInvalidFieldConfigSchemesForIssueTypeRemoval

Returns a collection of FieldConfigSchemes for all Configuration
Contexts that will become invalid after the issuetype has been removed. That is the configuration contexts that
will no longer be linked to ANY issue types after the issue type passed is has been deleted.